The present invention relates to the manufacture of dental bridges of aluminium oxide, which is currently one of the preferred materials for this purpose. A practice has been developed by which the dentist prepares the two supporting teeth (implants) as anchors for the intended bridge, and thereafter takes an impression of the relevant area by using a decidedly form-stable impression material, in that the impression shall subsequently be used for the manufacture of both a master model and a fireproof model.
The impression is transferred to a dental laboratory where a mould is made for the manufacture of a master model in hard plaster. A duplicate mould of the master model is made for later manufacture of an individual fireproof support model, a so-called “firing table”.
Hereafter, the bridge is modelled up in a three-part formation comprising the two bridge anchors and a connecting intermediate link (pontic), of which the latter can, however, be prefabricated, with certain directions concerning dimensions for the transition areas between the three sections. Thereafter, these transition areas are cut over with a plane cut in accordance with a more detailed direction regarding the angle, and the three parts are sent to a specialist for the manufacture of the bridge parts in tightly-sintered aluminium oxide. However, in modern practice it is a preferred alternative that a three-dimensional scanning be carried out of the mould of the bridge parts, whereby one can suffice with a quick electronic transmission of the relevant scanning data to said specialist, who subsequently reproduces the parts in aluminium oxide.
The dental laboratory will then receive the three bridge parts which, after a possible grinding-off of excess material, are temporarily joined together, e.g. with cyanailite glue, after which a fireproof “pilot model” of the bridge is made. The already-mentioned individual “firing table” is also made for use as support element in the subsequent firing of porcelain on the assembled bridge. The fireproof material is allowed to set, after which both models are placed in a special kiln for degassing, which must be programmed in accordance with the directions for the selected fireproof material.
With the known technique, use is made of glass powder as a binding agent, which in aqueous suspension is formed as a ball which is placed on top of the relevant assembly areas, after which the glass is activated by suitable heating in an ordinary porcelain kiln, in that the glass is hereby sucked down between the assembly areas.
The thus assembled bridge frame is removed for final processing. During the subsequent, ordinary porcelain firing, the item must be supported on the said, pre-prepared “firing table”, in that the glass binding in the assembly areas becomes unstable at the firing temperature.
It has been ascertained that although it is used to a wide extent, this method is not particularly ideal, in that it is very work-demanding and results in products which have a breaking strength which is not satisfactory. Many attempts have been made to improve it, but hitherto without significant results. Primarily, the solution will be to find an improved binding agent, but although highly-developed binding agents and great expertise already exist in the dental field, the result has always been that the “molten glass” has hitherto remained the agent which is used.